Preliminary treatment is performed to optimize the use of membranes and increase membrane operating time. During this operation, water is prepared to pass through the membrane.

Osmosis is the movement of a solvent from a dilute solution to a concentrated solution through a semipermeable membrane. Reverse osmosis is a widely used separation technique with a variety of applications. Desalination of seawater and separation of organic and toxic substances from industrial wastewater are two important applications of this technology.